On Sat, 3 Sep 2005 09:50:43 -0500, "hasan schiers"
wrote:

I do have correlation now. The vswr meters and the mfj all read the same
resonant frequency now, Wes. See my post that shows the data for 0,2,4,8
radials. While a given absolute value might be in error (a certainty due to
inexpensive instruments), the trend is sound for bandwidth, but a bit
strange for feedpoint impedance. (BW is narrowing but input Z is going up,
with increasing numbers of radials.)

Ideas?

Well, I think that you're expecting the thing to behave just like a
monopole but it's not a monopole.

When I model your configuration (except for insulation) I get a
resonant freq of 3.573 MHz and R = 23.3 ohm over a Mininec Pastoral
ground.

Making it a full height monopole it must be 67' high and the feedpoint
R = 37.

I believe that I read elsewhere that you are taking data at the input
end of a coax line. Unless you have characterized the line and are
backing out its effects you are going to remain mystified.

Also it you have any other antennas in the area that can be an issue.

I'm a believer in modeling but unless -everything- is accounted for,
reality and the model won't correlate.

For example, I have a Cushcraft AV-80 vertical that I've used as a
test bed. This is a 2" diameter, 36' high pipe with four 3' top hat
wires. Cushcraft supplied a base-loading coil, which is not used.
The antenna is ground-mounted on a 16" square aluminum plate with
sixteen 50' radials. Installing radials at this location is a
"sticky" proposition and the soil is best characterized as sand
(decomposed granite actually).

I have measured the base impedance with both an HP8405 Vector
Voltmeter and coax bridge that was calibrated with an open-short-load
(OSL) method as well as a much faster N2PK vector network analyzer,
calibrated the same way. All measurements were taken at the base of
the antenna. This is an on again off again project (currently off)
with the goal of determining the effectiveness of the radial field.

The data are very repeatable and believed to be correct; however, I
cannot construct a model that replicates the physical antenna. For
example the curve on the Smith chart of the measured data has a little
bump in it and the resonant frequency is slightly off from the model.
The "bump" isn't a full-blown resonance loop, but it looks like it's
trying. Here is a plot from 1.5 to 15 MHz. The resonant freq is 5.5
MHz.

http://users.triconet.org/wesandlinda/Vertical_Z.gif

As you can see from the photo, there several other "verticals" in the
vicinity as well as my 45' foot tower with beam and wire dipoles 90'
away.

http://users.triconet.org/wesandlinda/Vertical_4.jpg